[BC] Interesting Phenomena With WWDB 860

[Thomas G. Osenkowsky]

What you are hearing is a function of pattern bandwidth.
Pattern bandwidth refers to the change in radiation
pattern with frequency. When you change frequency, the
following all change:

Electrical tower height, efficiency, and spacing. The
self and mutual impedances change. In the
phasing/coupling system transmission line electrical
length, attenuation, capacitive and inductive reactance.

Ideally, the pattern should remain constant with change in
frequency. Most times, this is not the case. When the
sidebands are not attenuated, or asymmetrically attenuated
distortion will result. The greater the carrier attenuation with
less sideband attenuation, overmodulation results. You hear
this same phenomenon with selective fading.

Computer modeling of arrays and feeder systems allows
the designer to analyze pattern and impedance to minimize
this effect. When you have deep nulls many make the assumption
that the number of listeners in those areas are minimal. In
designing optimized systems sometimes compromises are
necessary. Older arrays have probably not been optimized
either due to cost or the lack of interest.

Tom Osenkowsky, CPBE